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Can singing really break glass?

We’ve all seen it on TV and in the movies, the talented opera singer reaching the high note and suddenly champagne glasses and windows shatter into a million pieces. But can it happen in real life?

In theory, yes, since everything has its own natural frequency. An object’s natural frequency is the frequency at which it will vibrate when disturbed (hit, struck etc). This is also known as its resonant frequency. If the surroundings of an object vibrate at this same frequency, then the object will visibly vibrate. If you blow across the top of a glass bottle, you can sometimes get a note when the air in the bottle neck resonates against the air in the main part of the bottle.

On a large scale, this can happen with huge structures, such as bridges. There was a famous case in 1940 with the Tacoma Narrows Bridge. There was a gale and the air was oscillating at a frequency that matched the natural frequency of the bridge. The bridge began to violently vibrate and finally collapsed.

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So, back to the glassware, if a bridge can break because of wind then surely a glass can break from a musical note. To start with, it needs to be a glass with a strong resonance – so when you ping it with a finger it should easily make a ringing noise. This means it is capable of vibrating more than other glasses. The thinner the glass, the more likely it is to break too, for obvious reasons. Careful now!

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Now for the tricky part: the musical note must be at the exact same frequency of the glass. However, the note also needs to be amplified quite loud otherwise it won’t work either. For the glass to shatter, there must also be teeny-tiny microscopic defects or cracks to initialise the break in the first place. The fracture grows from these cracks until it is enough to break the glass altogether. So, with the correct frequency and a lot of luck…SMASH! Maybe…It’s not as easy in practice as it is in theory! Basically, it is possible to shatter glass just using sound – but it is very difficult!

Just don’t try it with your mum’s or grandma’s best crystal wine glasses though – eh?!

 

If you’re fascinated by how sound works, why not choose A-Level Maths and Physics? To learn more about the connection between music and science, read this article